For the Health of It
Equine botulism is most frequently observed in Kentucky and the Mid-Atlantic region of the Eastern United States , although it has been reported worldwide . The disease is also known as shaker foal syndrome , forage poisoning , and grass sickness .
Botulism is a neuromuscular disorder of horses caused by neurotoxins of the bacteria Clostridium botulinum that results in flaccid paralysis by the action of the various botulinum neurotoxins in the presynaptic axon , preventing release of acetylcho- line into the synapse . Of the three types , botulism Type B occurs throughout the United States but is more predominant in the Mid-Atlantic states and Kentucky . Type A botulism occurs primarily in the west while botulism type C occurs in Florida . Botulism neurotoxins type B and C are the most commonly reported types in foals .
Botulism results from exposure to the toxin by three main routes . Ingestion of pre-formed toxin is the most common form affecting adult horses when they eat feed , such as hay or grain , that contains animal remains . Swallowing the botulism organism with subsequent elaboration of toxin in the intestines is known as shaker foal syndrome , which is associated with one- to three-month-old foals , but can occur as early as one week of age . Rarely , wound infection with Clostridium botuli- num occurs and the subsequent release of the toxin in the body causes disease .
Clinical signs after exposure to toxin occur from 12 hours to several days and may be dependent on dose and type of botulinum neurotoxin involved . Sudden , unexplained death of one or more horses may be the initial signal of an outbreak . Decreased eyelid , tongue , and tail tone may be observed early in disease . Horses that can walk may have a stilted , short-strided gait without ataxia . Muscle trembling and weakness may be apparent , particularly in foals . Pupillary dilation with sluggish pupillary light reflexes and difficulty swallowing ( dysphagia ) is fre- quently observed . Clinical signs may rapidly progress to recumbency . Tachycardia may occur , particularly in foals . Death is generally attributed to respiratory failure secondary to respiratory muscle paralysis . 8 • Walking On
Equine Botulism
Reprinted with permission from Volume 23 , Number 2 of Equine Disease Quarterly
Diagnosis is made based on clinical signs . Definitive diagnosis requires detection of the toxin in serum , feces , gastrointestinal ( GI ) contents , or feed by enzyme-linked immunosorbent assay ( ELISA ), radioimmunoassay ( RIA ) or polymerase chain reaction ( PCR ). Specific toxin activity can be confirmed by a mouse inoculation test and is sup- ported by isolation of C . botulinum from serum , feces , GI contents , or feed .
Treatment consists of blockade of any cir- culating toxin by intravenous administration of plasma containing specific antibotulism neurotoxin antibodies ( generally against types B and / or C ). Supportive care , including fluid , nutritional , antimicrobial and respiratory supportive therapies , is critical . Adults and foals with mild respiratory signs can frequently be treated with intranasal oxygen insufflation and positioning in sternal recumbency . Mechanical ventilation can be life-saving in foals . Antimicrobial administration ( avoiding procaine penicillin , aminoglycosides , and tetracyclines ) is employed to prevent or reduce complications of the disease , such as aspiration pneumonia caused by dysphagia . Nutritional management can be provided to foals by feeding milk or milk replacer via indwelling nasogastric or nasoesophageal tubes while in adult horses , periodic nasogastric intuba- tion of slurry meals or commercially available liquid diets can be provided .
For type B botulism , the survival rate in ap- propriately treated foals less than six months of age is greater than 90 %. Affected adult horses that remain standing have a good prognosis , although a prolonged recovery , while recumbent adults are less likely to survive . Vaccination with Clostridium botulinum type B toxoid is thought to be almost 100 % protective against type B in adult horses and should be undertaken in endemic regions . Vacci- nation of pregnant mares will be at least partially protective to their foals assuming adequate passive transfer of immunity .
CONTACT :
Dr . Pamela Wilkins ( 217 ) 333-2000
pawilkin @ illinois . edu University of Illinois College of Veterinary Medicine Champaign-Urbana , Illinois